Polychlorosilanes are well known in the art and were first prepared over one hundred years ago. The methods of preparation are varied as are the types of polychlorosilanes that are prepared by such methods. Two major types of polychlorosilanes exist for our interest herein, the first is the homologous series Si.sub.n Cl.sub.2n+2 which can be compared superficially to the carbon series C.sub.n H.sub.2n+2. The second type is the silicon subchlorides wherein the chlorine to silicon ratio is below that of the homologous series i.e. (SiCl.sub.2).sub.n or (SiCl.sub.1.5).sub.n.
In the first type, almost all of the published literature deals with polychlorosilanes wherein n has a value of 6 or less. For example, Troost and Hautefeville, Ann. Chim. Phys. (5) 7 459(1871) describe the reaction of silicon metal with silicontetrachloride at or above 1000.degree. C. to prepare Si.sub.2 Cl.sub.6. Friedel, Compt. rend.; 73 1001 (1871) reported that chlorine or mercuric chloride and hexaiododisilane produced Si.sub.2 Cl.sub.6. Several other researchers also found routes to Si.sub.2 Cl.sub.6 that were based on chlorosilanes viz. J. B. Quig, J. H. Wilkinson; JACS 48 902-6 (1926); J. Nichl; German Patent 1142848 (1963) E. ENK, Besson and Fournier; Compt. rend. 152 603 (1911).
The subchlorides, (SiCl.sub.1.5).sub.x have also been reported on by Besson and Fournier and others. In general, however, little is known of the structures of these subchlorides because characterization has routinely involved a simple Cl/Si ratio.
In all of the prior work, however, no mention has been made of utilizing these polychlorosilanes to obtain silicon metal through pyrolysis.